1) Field of the Invention
The present invention relates to a method and apparatus for spinning bicomponent filaments. More particularly, the invention relates to a spinneret used for bicomponent spinning. The spinneret has a plurality of holes wherein the density of holes increase radially outward from the center of the spinneret.
2) Description of Prior Art
Bicomponent filaments of the sheath/core configuration are well-known and a variety of spinning packs and spinnerets have been employed in the production of textile filaments. A conventional spinning assembly involves feeding molten sheath forming material to the spinneret holes, in a direction perpendicular to the holes, and injecting molten core forming material into the sheath-forming material as it flows into the spinneret holes.
There are several prior art hole layouts for bicomponent spinnerets. One is providing the same number of holes per row. This configuration is typically used for low hole density/high denier per filament (dpf). Another is a constant hole density wherein there are a different number of holes per row and the hole density is constant by having the hole to hole distance in the same row, and row to row distance, constant. This configuration is typically used for high hole density/low dpf. Both of these configurations have the disadvantage that the hole density is higher towards the center of the spinneret than the outer portion of the spinneret, or remains constant throughout the spinneret. Consequently, quench air radiating outward from the center of the spinneret has difficulty reaching filaments in the outer rows. Filaments in the interior rows are quenched first and, therefore, solidify and crystallize before filaments in the outer rows. This causes a distribution in filament uniformity with spun orientation and filament diameter (dpf) according to which row the filament is in.
A distribution of spun yarn orientation is undesirable since this causes broken filaments in the subsequent drawing operation. Thus, when each filament has substantially the same spun orientation, the filaments can be drawn at a high draw ratio without broken filaments. Additionally, by uniformly quenching filaments, conversion is higher, that is, the equipment can be run faster with less stoppage and waste.
Accordingly, there is a need for an improved spinneret wherein the density of holes increase radially outwards from the center of the spinneret and are positioned such that filaments are uniformly quenched and have a higher uniformity in spun orientation than prior art devices.
The present invention is directed towards a spinneret assembly and method for spinning bicomponent filaments which are substantially uniformly quenched and have a generally uniform spun orientation so that filaments can be drawn with less waste. The spinneret accomplishes this result by arranging spinneret holes in a generally parallelogram pattern having a constant diagonal distance between holes such that the hole density increases in the direction away from the center of the spinneret thereby ensuring that radial quench air uniformly reaches all the filaments.
According to the present invention, the spinneret assembly includes a distributor and a spinneret. The distributor is provided with separate flow passages to convey core polymer and sheath polymer to the spinneret. The spinneret is provided with a plurality of bosses, each having a hole, which coaxially align with the distributor core passages for receiving the core polymer. The holes are arranged in increasing density from a center position of the spinneret to an outer edge of the spinneret.
According to another aspect of the present invention, the holes are arranged in curvilinear rows and the distance between a hole in one row to a nearest hole in an adjacent row is constant for all such pairs of holes.
According to a further aspect of the present invention, the holes in alternative rows are radially aligned.
According to still another aspect of the present invention, the distance between succeeding rows decreases radially from a center position to an outer edge of the spinneret.
According to another aspect of the present invention, a method is provided for making a bicomponent filament. The method includes providing a distributor having separate flow passages for core polymer and for sheath polymer. A spinneret is provided with bosses and is secured beneath the distributor. Holes are placed in the bosses which extend through the bosses and the spinneret. The holes are coaxially aligned with the core polymer passages. Moreover, the holes are arranged in curvilinear rows and in increasing density in a radial direction from the center of the spinneret to an outer edge of the spinneret. Molten core polymer and molten sheath polymer are supplied to the distributor, forced through respective passages, to the spinneret. The molten core polymer flows through the spinneret holes. The molten sheath polymer flows over the bosses and through the holes forming a sheath about the core polymer. The sheath-core polymer is then substantially uniformly quenched.